This invention relates to the field of dental restorations, and in particular to the field of composite resin restorations including those in cervical, occlusal or posterior interproximal sites. Composite dental restorative materials are described in U.S. Pat. No. 3,066,112, issued in November 1962. Current practice in filling cavities with cosmetically appealing compostions involves the use of resins mixed relatively homogeneously with a very finely divided or colloidal filler and inserted into the dental cavity. Demand has increased for placement of composite restorations in posterior teeth. There are a number of factors that contraindicate the use of the composite (resin plus filler) compositions for occlusal or posterior interproximal restorations. Some of these include the problem of polymerization shrinkage, which can result in contraction gaps and microleakage of gingival margins of restorations; a low stiffness (modulus of elasticity), which can result in loss of support of remaining tooth structures; and loss of restoration contour where contacted by cusps of the opposing dentition, which can lead to malocclusion. This latter problem is the most serious; the composite resin restorations tend to crack, break down and wear away where the cusps of opposing teeth contact or closely approach the restorations.
Composite resin dental materials of this type are, for example, described in U.S. Pat. No. 4,215,033, issued July 29, 1980, and in Bowen et al., "Semiporous Reinforcing Fillers For Composite Resins: I. Preparation of Provisional Glass Formulations," 55 J. Dent. Res. 738-47 (1976), and Bowen et al., "Semiporous Reinforcing Fillers For Composite Resins: II. Heat Treatments and Etching Characteristics," 55 J. Dent. Res. 748-56 (1976). See also, Bowen et al., "Theory of Polymer Composites," International Symposium on Posterior Composite Resin Dental Restorative Materials, 95-107 (Peter Szulc Pub., The Netherlands, 1985), and references cited in each of the above articles and patent.
U.S. Pat. No. 4,215,033 in particular describes a transparent glass filler material in which the glass is separated into two interconnected vitreous phases which after crushing and ball milling to a very fine powder, is acid etched to produce a porous surface layer. Preferred glass compositions disclosed in this patent include a mixture of silicon dioxide, boron oxide, aluminum oxide and strontium oxide, with one or more from the group of calcium oxide, zinc oxide, stannic oxide, and zirconium oxide as optional modifying ingredients. The transparent inorganic glass particles of microscopic size are silane treated and then combined with an organic resin to provide an improved composite dental material.